DHF—also referred to as heart failure with preserved ejection fraction (HF-PEF)—is a condition wherein systolic heart function is generally preserved but diastolic function is compromised, i.e. there is a significant degree of diastolic dysfunction. Diastolic dysfunction generally refers to an abnormality in the ability of the heart to fill during diastole, which is the phase of the cardiac cycle when the ventricles relax and fill with blood prior to contraction. At present, implantable medical devices are not adequately equipped to treat DHF. However, clinical evidence is emerging that CRT may show benefit in the DHF patient population. Some early CRT studies have shown the benefit of CRT therapy for patients inadvertently included in CRT trials with significant improvements in functional class and symptoms. [See, Cleland et al., “Long-term effect of cardiac resynchronisation in patients reporting mild symptoms of heart failure: a report from the CARE-HF study”, Heart 2008; 94:278-283] An additional recent publication from the PROSPECT trial found that 24% of patients had an ejection fraction (EF) below 35% and, even though this group had lower left ventricular (LV) volumes and shorter surface electrocardiogram (ECG) QRS duration, outcomes were not significantly different from the low EF group. [See, Chung et al. “Cardiac resynchronization therapy may benefit patients with left ventricular ejection fraction >35%: a PROSPECT trial substudy”, EJHF 2010; 12:581-587 and Penicka et al. “Cardiac resynchronization therapy for the causal treatment of heart failure with preserved ejection fraction: insight from a pressure-volume loop analysis” EJHF 2010; 12:634-636] This included reduced left ventricular (LV) end diastolic volumes, which are associated with a mortality and morbidity benefit. [See, Yu et al. “Left Ventricular Reverse Remodeling but Not Clinical Improvement Predicts Long-Term Survival After Cardiac Resynchronization Therapy” Circ 2005; 112:1580-1586.]
Programming of the atrioventricular (AV) interval in CRT patients has been shown to benefit outcomes of patients. The effects of intra-atrial delay based on the position of a right atrial (RA) lead has been shown to be potentially deleterious to patient outcomes causing intra-atrial dyssynchrony similar to that seen in the ventricles. [See, Maass et al. “Importance of Heart Rate During Exercise for Response to Cardiac Resynchronization Therapy” JCE 2009; 20:773-780.] Left atrial size (thus intra atrial delay) has also been shown to have an impact on the progression of congestive heart failure (CHF) specifically DHF. [See, Gottdiener et al. “Left Atrial Volume, Geometry, and Function in Systolic and Diastolic Heart Failure of Persons >65 Years of Age (The Cardiovascular Health Study)” Am J Cardiol 2006; 97:83-89.] Careful optimization of AV timing has been shown in numerous studies to benefit diastolic parameters. [See, for example, Chan et al. “Tissue Doppler Guided Optimization of A-V and V-V Delay of Biventricular Pacemaker Improves Response to Cardiac Resynchronization Therapy in Heart Failure Patients” J of Cardiac Failure 2004; 10, 4 (suppl.): S72 (abstract 199); Bordacher et al. “Echocardiographic Parameters of Ventricular Dyssynchrony Validation in Patients With Heart Failure Using Sequential Biventricular Pacing” JACC 2004 44 11 2175-2165; O'Donnell et al. “Long-term variations in optimal programming of cardiac resynchronization therapy devices” PACE 2005; 28:S24-S26; and Zhang et al. “The role of repeating optimization of atrioventricular interval during interim and long-term follow-up after cardiac resynchronization therapy” Volume 124, Issue 2, 29 Feb. 2008, Pages 211-217). In addition, a large group of DHF patients suffer from chronotropic incompetence, which can be readily addressed via otherwise conventional atrial pacing (i.e. atrial pacing wherein stimulation pulses are delivered to the right atrium (RA) via an RA lead.) Note that the presence of chronotropic incompetence has also been shown an important predictor to CRT response. [See, Borlaug et al. “Echocardiographic Parameters of Ventricular Dyssynchrony Validation in Patients With Heart Failure Using Sequential Biventricular Pacing Impaired Chronotropic and Vasodilator Reserves Limit Exercise Capacity in Patients With Heart Failure and a Preserved Ejection Fraction” Circ. 2006; 114:2138-2147]
Nevertheless, there is still a significant need to provide effective pacing techniques for use by implantable medical devices within DHF patients and it is to this end that aspects of the invention are generally directed.